A highway may contain several types of roads, but the highway will continue to have the same route number. Primary roads have numbers 1 to 99. Secondary roads are numbered 100 to 299. Municipal (tertiary) roads are numbered 300 to 9999.[3]

These Interstate Highways run along tollways and roads that are not grade-separated, which means drivers must use a specially made group of ramps to get to the road. There are no signs for these Interstate Highways. They are signed as Puerto Rico routes.

Puerto Rico's interstate routes are not to be confused with Puerto Rico Routes PR-1, PR-2, and PR-3. These are other major highways in Puerto Rico.